Abstract
We isolated and characterized a novel K-Cl cotransporter, KCC3, from human placenta. The deduced protein contains 1,150 amino acids. KCC3 shares 75-76% identity at the amino acid level with human, pig, rat, and rabbit KCC1 and 67% identity with rat KCC2. KCC3 is 40 and 33% identical to two Caenorhabditis elegans K-Cl cotransporters and approximately 20% identical to other members of the cation-chloride cotransporter family (CCC), two Na-K-Cl cotransporters (NKCC1, NKCC2), and the Na-Cl cotransporter (NCC). Hydropathy analysis indicates a typical KCC topology with 12 transmembrane domains, a large extracellular loop between transmembrane domains 5 and 6 (unique to KCCs), and large NH(2) and COOH termini. KCC3 is predominantly expressed in kidney, heart, and brain, and is also expressed in skeletal muscle, placenta, lung, liver, and pancreas. KCC3 was localized to chromosome 15. KCC3 transiently expressed in human embryonic kidney (HEK)-293 cells fulfilled three criteria for increased expression of K-Cl cotransport: stimulation of cotransport by swelling, treatment with N-ethylmaleimide, or treatment with staurosporine.
Highlights
IntroductionThe primary protein structure of the Na-Cl cotransporter, or NCC, was first characterized from flounder urinary bladder [9] and subsequently in rat renal cortex [8]
NKCC1 is widespread among many tissues where it is primarily involved in regulation of cell volume
NKCC2 is apparently restricted to apical membranes in kidney, where it is involved in NaCl reabsorption and the concentration of urine by the countercurrent multiplier
Summary
The primary protein structure of the Na-Cl cotransporter, or NCC, was first characterized from flounder urinary bladder [9] and subsequently in rat renal cortex [8]. The protein structure of the Na-K-Cl cotransporter (NKCC1) was first described from shark rectal gland [37] and was subsequently characterized from mouse kidney [4] and human colon [32]. NKCC1 promotes regulation of cell volume [27]. Another isoform of the Na-K-Cl cotransporter, NKCC2, which is kidney specific, was characterized from rat outer medulla [8] and from rabbit kidney [30]. NKCC2 is apparently restricted to apical membranes in kidney, where it is involved in NaCl reabsorption and the concentration of urine by the countercurrent multiplier
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